How to developp Custom Forms for Workflow task ?

Today there is only on Custom Form available (M3) or no forms : 

If we selected M3 , no attributes could be displayed ??? so what is the purpose of M3 forms ? , and if we do not use M3 Forms , we can display/edit information but the ergonomy still strange : large space for description and small space for relevant information displayed  if you are using Task Notification , but if your are usingt Task list Widget , everything is ok but impossible to have the right size with al fields .